2022 MPFG Problem19

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Problem

Let $S_-$ be the semicircular arc defined by \[(x+1)^2 + (y-\frac{3}{2})^2 = \frac{1}{4} and x \leq -1.\] Let $S_+$ be the semicircular arc defined by \[(x-1)^2 + (y-\frac{3}{2})^2 = \frac{1}{4} and x \leq -1.\]

Let $R$ be the locus of points $P$ such that $P$ is the intersection of two lines, one of the form $Ax + By = 1$ where $(A,B) \in S_-$ and the other of the form $Cx + Dy = 1$ where $(C, D) \in S_+$. What is the area of $R$? Express your answer as a fraction in simplest form.

Because $Ax+By=1,Cx+Dy=1 ==> (A,B),(C,D)$ is a solution set of $xX+yY=1$, which means that the $2$ coordinates are on the line of $xX+yY=1$